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2002 2500hd brake question...

Discussion in 'Chevy Trucks' started by buckhigh, Nov 4, 2012.

  1. buckhigh

    buckhigh Senior Member
    Messages: 183

    When I come to almost a complete stop, my abs is kicking in whether the ground is wet or dry. No dummy lights are coming on the dash. I want to do all 4 brakes before winter. Calipers are only 2 years old. Are the sensors dirty? Bad? Truck has 120k miles so I would rather replace than clean. Are the sensors located on the caliper?

    Thanks for the help!
     
  2. maverjohn

    maverjohn Senior Member
    Messages: 902

    The sensors are in the wheel bearing, The bosses truck started doing the same thing and we had to replace both front bearings.
     
  3. buckhigh

    buckhigh Senior Member
    Messages: 183

    Thank you!
     
  4. theholycow

    theholycow PlowSite.com Addict
    Messages: 1,180

    A complete discussion of it is in this recent thread:
    http://www.plowsite.com/showthread.php?t=138976
    I posted a detailed howto after having done it just recently.

    If your budget is good enough for replacing the bearings, go ahead and do that. Don't get cheap ones. Get AC Delco or Timbren. If not, and if your bearings test good, it may not be entirely necessary but you won't get brand new sensors cheap; gotta grab them at the junkyard unless you catch a good deal at something like discountpartshub.com.
     
  5. buckhigh

    buckhigh Senior Member
    Messages: 183

    Thanks for the link. My hub assemblies were replaced 3 years ago, and carry a lifetime warranty (AC Delco). Your link says they come with new sensors? Is it common for sensors to go bad in 3 years?
     
  6. mikes-plow

    mikes-plow Senior Member
    Messages: 103

    ya major design flaw for gm. if you dont mind the lights on the dash the cheapest fix is to just pull the ABS fuse out. you could go broke changing bearings just to have abs, thats why i said F-it and just pulled the fuse until this set of bearings goes bad. 3 years is about how long mine last as well
     
  7. theholycow

    theholycow PlowSite.com Addict
    Messages: 1,180

    It is a common issue. It's just corrosion at the mounting surface (though if you ignore it long enough the sensor gets messed up too). You can help prevent it with common anti-corrosion tactics, I guess. I just left mine covered in a lot of grease, if I have to take it apart and clean it once every couple years, no big deal.

    You don't need to replace the whole hub assembly if the hub/bearing is working fine and the only issue is a failed sensor. Go to a self-service junkyard and harvest a few ABS sensors; test them before you bother pulling them. I have a spare now so I won't even have to go to the junkyard the next time one goes bad, but I think if I just fix the problem as soon as it happens by cleaning the corrosion then my sensors won't go bad anyway.

    Your sensors may be fine. You may just need to clean off the corrosion and they'll work right again.

    Pulling the ABS fuse doesn't only cause the light to light up on your dash, it also disables ABS. If you don't like ABS (and don't have state inspections that check for it) then go ahead and do that. Mine can't be disabled if I want to pass inspection, and anyway I prefer letting the computer detect a single wheel turning slower and having it pump the brakes 30 times per second (or whatever) on just that one wheel instead of me pumping all 4 brakes at human speed when I realize that a wheel has been skidding.
     
  8. theholycow

    theholycow PlowSite.com Addict
    Messages: 1,180

    A couple more thoughts:

    I may be wrong about it braking only the guilty wheel; I know the latest vehicles do but I don't know if my 2002 model does. Either way the computer can detect it sooner and pump the brakes more accurately and a whole lot faster than my foot can.

    Since your parts have a warranty, I'd say just try cleaning the corrosion, and if the sensor is bad don't bother harvesting sensors at the junkyard, just get an entire replacement hub/bearing unit. It's not like these last for the life of the vehicle, you'll probably need to replace it again in a year or two anyway.
     
  9. Woodenshoe

    Woodenshoe Member
    Messages: 84

    If I'm not mistaken, pulling the ABS fuse also effects the proportioning valves as well... Your better off unplugging one of the wheel sensors which will automatically disable the ABS system.
     
  10. theholycow

    theholycow PlowSite.com Addict
    Messages: 1,180

    Interesting. I thought the non-ABS functions of the proportioning valve were completely mechanical.
     
  11. affekonig

    affekonig Senior Member
    Messages: 909

    This condition is covered in a well-known recall (05068C). Get a hold of a dealer and they should take care of it.
     
  12. Woodenshoe

    Woodenshoe Member
    Messages: 84

    Dynamic Proportioning...
     
  13. maverjohn

    maverjohn Senior Member
    Messages: 902

    Hey theholycow, How do you test the sensor ?
     
  14. brad96z28

    brad96z28 PlowSite.com Addict
    Messages: 1,526

    Easy and correct way is with a lab scope.
     
  15. theholycow

    theholycow PlowSite.com Addict
    Messages: 1,180

    No scope is necessary. Reach behind and unplug sensor from harness near frame/upper control arm. Connect multimeter set to AC millivolt range. Jack that corner and spin the wheel by hand as fast as you can. You should get at least 350mv (I got 1.5v on a brand new sensor). If not, you've found the guilty wheel...first try cleaning the corrosion at the mounting surface and test again, if it fails again then replace.
     
  16. brad96z28

    brad96z28 PlowSite.com Addict
    Messages: 1,526

    Im sure you can pick up a glitch with a multi meter :laughing: Lots of ways you can test I just recomended the correct one. They also have wheel speed sensor testors but you can not catch a bad wave form with one. Check enough you will know what works best.
     
    Last edited: Nov 5, 2012
  17. theholycow

    theholycow PlowSite.com Addict
    Messages: 1,180

    The AC 350mv test is direct from the GM TSB, and the GM service manual's normal procedure is similar. Perhaps it may be possible for this sensor to fail in such a way that it provides the correct voltage with a messed up wave form, but this test is sufficient to find out which sensor is at fault for the symptom in question.
     
  18. brad96z28

    brad96z28 PlowSite.com Addict
    Messages: 1,526

    Trust me there is such a way and happens all the time. Not just wtith wheel speed sensors. Many of the sensors should be tested with a scope. Spikes and bad patterns can not be seen with a multi meter. And it will show a very bad patern with the rust build up.
     
  19. theholycow

    theholycow PlowSite.com Addict
    Messages: 1,180

    Ok, so if you fail to identify the guilty wheel with the procedure that GM recommends, you could find yourself a scope to borrow. I've never heard of the GM procedure failing to identify the fault but it's certainly possible. There's no need to go out and buy a scope for this until the normal tests have failed to identify the problem.
     
    Last edited: Nov 6, 2012
  20. tuney443

    tuney443 PlowSite.com Addict
    Messages: 1,847

    Holycow is correct.Remove your sensors,clean off the rust with a NEW razor blade on your favorite scraper,use some plumbers crocus cloth or fine sandpaper to get the hub area shiny clean,apply a THIN film of grease to keep future corrosion at bay,clean off plastic,reassemble.Just the extremely slight additional clearance caused by the rust will cause your problem,by eliminating it,you will be back to specs and your issue will be gone.